Reflux vacuum filters of the aforementioned type are known. One device of this type is marketed by the company ARGO-HYTOS GmbH and is commercially available under the type designation E084. Reflux vacuum filters are used in hydraulic systems having both an open hydraulic circuit (such as working hydraulics) and a closed hydrostatic system (for example, a traveling mechanism). Reflux vacuum filters can assume both the function of the reflux filter of the open circuit and the function of the vacuum filter of the closed circuit (mechanism), assuming that the reflux flow of the open hydraulic system is not smaller than the volumetric flow of the feed pump for the hydrostatic system.
In the operation of these devices, the reflux amount, for example, of the working hydraulics, is supplied to the filter and is purified by the filter medium of the filter element, and full-flow extremely fine filtration can take place. In the filtered fluid available to the feed pump of the hydrostatic system, a preload pressure is maintained by the back pressure valve and ensures that the amount of filtered reflux required by the feed pump of the compensator can be removed. Excess amounts travel via the back pressure valve to the tank connection and are drained towards the tank. At high dynamic pressures caused, for example, by fouling at the filter element, a pressure decrease takes place by triggering of the bypass valve.